At present all virt drivers provide a cleanup method that takes a single
destroy_disks boolean to indicate when the underlying storage of an
instance should be destroyed.
When cleaning up after an evacuation or revert resize the value of
destroy_disks is determined by the compute layer calling down both into
the check_instance_shared_storage_local method of the local virt driver
and remote check_instance_shared_storage method of the virt driver on
the host now running the instance.
For the Libvirt driver the initial local call will return None when
using the shared block RBD imagebackend as it is assumed all instance
storage is shared resulting in destroy_disks always being False when
cleaning up. This behaviour is wrong as the instance disks are stored
separately to the instance directory that still needs to be cleaned up
on the host. Additionally this directory could also be shared
independently of the disks on a NFS share for example and would need to
also be checked before removal.
This change introduces a backportable workaround configurable for the
Libvirt driver with which operators can ensure that the instance
directory is always removed during cleanup when using the RBD
imagebackend. When enabling this workaround operators will need to
ensure that the instance directories are not shared between computes.
Future work will allow for the removal of this workaround by separating
the shared storage checks from the compute to virt layers between the
actual instance disks and any additional storage required by the
specific virt backend.
Related-Bug: #1761062
Partial-Bug: #1414895
Change-Id: I8fd6b9f857a1c4919c3365951e2652d2d477df77
(cherry picked from commit d6c1f6a103)
8c678ae572